1. Field of the Invention
The present invention relates to a chip-type network resistor suitable for high density wiring.
2. Description of the Related Art
There has recently been used a chip-type network resistor shown in FIG. 3 as an alternative to individual chip resistors mounted side by side for wiring.
In the same drawing, separate electrodes 2 are formed on the opposite sides of an insulative substrate 1 made of ceramic by printing four areas of silver paste (or silver/palladium paste) on one of both sides of the insulative substrate 1, i.e., eight areas in total on both sides thereof. Each of resistance layers 3 is formed by printing on a position for connecting between the separate electrodes 2, 2 set in pair on the insulative substrate 1. Then, these resistance layers 3 are subjected to primary coating with glass material or the like, and thereafter trimming grooves (not shown) are defined in the resistance layers 3 by a means such as laser trimming, thereby adjusting the resistance values of the resistance layers 3. After a trimming process has been made, the so-adjusted resistance layers 3 are covered with an overcoat layer 4, as secondary coating, comprised of glass material or the like. After the overcoat layer 4 has been formed thereon, a nickel plating process for preventing silver from being excessively consumed and a solder plating process for ensuring wettability by solder are successively applied to the respective separate electrodes 2. However, since the plating material does not adhere to each of the resistance layers 3 which have been covered with the overcoat layer 4 at the time of such a plating step, there is no possibility of variations in preset resistance values, and moisture-proof characteristics are kept satisfactory.
If such a chip-type network resistor is used, a plurality of chip-type resistors is equivalently mounted as a single unit by simply mounting one chip-type network resistor, thereby greatly improving the workability. When the intervals defined between the adjacent resistance layers 3 on the insulative substrate 1 are reduced, the chip-type network resistor can be mounted even on a high-density type printed-wiring board in which the pitch between adjacent patterns is narrow.
In recent years, there have widely been used, as printed-wiring boards, those subjected to high density increasingly and in which the pitch between adjacent patterns is set to be narrowest. Thus, the chip-type network resistor of the above-described type is not suitable in many cases. In order to permit higher-density wiring or mounting, there has been proposed, as shown in FIG. 4, a chip-type network resistor of a type in which a plurality of resistance layers 3 each mounted between a common electrode 5 extending across an insulative substrate 1 and each of separate electrodes 2 are disposed on both sides of the common electrode 5 in a zigzag manner, and the thus-disposed resistance layers 3 are covered with an overcoat layer 4. However, this type of chip-type network resistor has the problem that the impedance of the common electrode 5 is slightly large and is susceptible to the influence of noise.